Fuel cells are energy conversion devices using an electrochemical reaction of a fuel with an oxidizing agent and convert chemical energy of the fuel into electric energy without converting the chemical energy into thermo-mechanical energy. Thus, generating efficiency of fuel cells is higher than that of conventional generating systems, and fuel cells are eco-friendly and are actively researched as a future power source.
Fuel cells may be classified into phosphoric acid fuel cells (PAFCs), polymer electrolyte membrane fuel cells (PEMFCs), molten carbonate fuel cells (MCFCs), direct methanol fuel cells (DMFCs), and solid oxide fuel cells (SOFCs) according to electrolyte and fuels used therein. Fuel cells have different operation temperatures, and materials for the fuel cells depend on the operation temperatures. PEMFCs have an operation temperature of about 80° C. PAFCs have an operation temperature of about 200° C. MCFCs have an operation temperature of about 650° C. SOFCs have an operation temperature of about 800° C.
Of these, SOFCs which are formed of only solid materials such as a ceramic or a metal have the highest energy efficiency, provide a wide choice of the solid materials, and are adapted for recycling waste heat.
For example, Japanese Patent Publication No. 2011-210568 discloses a fuel electrode collector unit of a solid oxide fuel cell.
FIG. 1 is an exploded perspective view illustrating main components constituting a solid oxide fuel cell in the related art. Referring to FIG. 1, a solid oxide fuel cell in the related art includes: a unit cell formed by sequentially stacking a cathode, electrolyte, and an anode; a separator plate disposed on the cathode; and a separator plate disposed on the anode.
Channels are formed in both surfaces of the separator plates. Although not shown in FIG. 1, a cathode collector is disposed between the cathode and the separator plate disposed on the cathode, and an anode collector is disposed between the anode and the separator plate disposed on the anode.
Air flows through channels between the cathode and the separator plate, and fuel gas flows through channels between the anode and the separator plate. Flows of reaction gas (the air and the fuel gas) induce oxygen or hydrogen ion conduction in an electrolyte layer, and an electrochemical reaction is generated on electrodes (the cathode and the anode), thereby generating electromotive force.
The air or the fuel gas is introduced into a side of the channels and is discharged from another side thereof. In other words, a fuel cell has inflow holes through which reaction gas is introduced, and outflow holes through which the reaction gas is discharged.
It is ideal that an electrochemical reaction uniformly occurs over an area across which reaction gas passes through a fuel cell. However in practice, reaction gas collects adjacent inflow holes, and a concentration of reaction gas near outflow holes is low. Thus, electricity is not uniformly generated over the entire area of a collector, and a large amount of electricity is generated in a portion of the collector near the inflow holes, and a small amount of electricity is generated in a portion of the collector near the outflow holes.
This decreases a current collecting efficiency of a fuel cell. In addition, since a reaction occurs more intensively at the inflow holes, the inflow holes are deteriorated more significantly than the outflow holes are.
Thus, although the outflow holes are slightly deteriorated, the significant deterioration of the inflow holes may significantly reduce the service life of the fuel cell.